Treating cellulose esters



Patented v Feb. 13, 1934 UNITED STATES TREATING CELLULOSE ESTERS Martin Marasco, Parlin, N. J assignor to Dupont Film Manufacturing Corporation, a corporation of Delaware N0 Drawing.

Application May 1, 1931 Serial No. 534,437

8 Claims.

This invention relates to cellulose ester prodnets and to an improved method for treating them. One object of this invention is to provide an improved transparent and substantially nonshrinking cellulose ester base for cinema film. Another object is to provide a novel method for rapidly ageing or preseasoning cellulose esters in the form of films or sheets. A further object is to provide an improved method for the rapid selective extraction of residual solvents from nitrocellulose products. Another object is to provide a method for controlling the shrinkage characteristics of cellulose ester film base. More specific objects will plainly appear from the de- 5 tailed description presented herein.

, creases the wear of the film during such operations as developing and projecting, as the result of the destructive action caused by the failure of the thus distorted perforations in the film to properly engage the sprockets in the various film machines. In color work and in many other photographic processes these changes in thesize of the film are extremely undesirable, and have serious and expensive consequences. 7

Therefore, I attacked the problem of removing harmful solvents and stresses before the film base is coated with light sensitive emulsion and preferably before the film is cut or fabricated for photographic uses. I determined that low boiling solvents are usually more soluble and diffuse out of the base more rapidly than those having relatively high boiling points and that therefore. these low boiling solvents are the ones to be extracted. Some solvents may be removed by soaking the film for long periods in cold water and the time can be somewhat shortened by gradually increasing the temperature of the water bath as the process of extraction advances. However, if hot water is used the presence of low boiling solvents in the film causes cloudiness therein commonly known as blushing, which is the result of the precipitation of nitrocellulose or cellulose acetate.

This blush is readily noticed if the low boiling solvents are allowed to remain in the film or if they are improperly extracted therefrom. To reduce the time required for the removal of the residual acetone, the film may also be subjected to long drying at relatively high humidity and temperature.

These prior general methods just discussed have been formerly used to hasten the drying of nitrocellulose powder and to accelerate the seasoning of celluloid sheets, but they are all obviously too slow for practical use. Furthermore included in the residual solvents remaining after the usual prior drying of film is one or two per cent of acetone that remains'in solid solution with the cellulose ester, the plasticizer and other high boiling solvents which have prevented the acetone from being thoroughly driven out by prior methods.

I have invented a novel method for the rapid removal or" low boiling residual solvents from nitrocellulose or cel'luose acetate films or sheets wherein these solvents are tenaciously held in solid solution and have produced novel results from this invention.

My improved method consists of first passing 7 the film base through a bath consisting of a selected solvent or mixture of solvents. The solvent or solvents used in this bath preferably have the following characteristics- 1. A rapid extracting action on the low boiling residual solvents in the film.

2. No objectionable solvent action on the cellulose acetate or cellulose nitrate film.

3. Only a slight swelling action thereon.

When nitrocellulose film base is being treated by my method, I prefer to have this bath consist of a solution containing approximately methanol, preferably approximately 90% meth-. anol and 10% water. This bath may be used at room temperature although if it is desired to further accelerate this process a temperature somewhat below the boiling point of the methanol may be used. In place of the methanol a mixture of methyl and ethyl may be used or ethyl alone may be substituted for the methanol. In fact this bath may be described as one consisting of a solution of alcohol so diluted that it will have only a swelling action on the film base and no solvent action thereon, but which will have an extracting action on the low boiling solvents contained in the film base.

After the film is treated in the bath having the characteristics just described the film is pref-,

erably then dried under only enough tension to prevent wrinkling while drying.

Further correction may be obtained by conducting this drying operation with the film under a known strain and subsequently releasing this strain by subjecting the film thus dried to an additional bath in a selected solvent that will have no swelling action thereon. The additional bath just mentioned may be of water at 100 F. to approximately 212 F. in temperature or it may be hot, moisture-saturated air at approximately 212 F. The time of this corrective treatment may be varied from a few minutes to approximately one hour depending on the shrinkage correction desired. During this hot bath treatment the strain or tension on the film may be regulated and controlled so as to give the finished film base controlledor predetermined shrinking properties. The more strain put on the film during this treatment the greater will be the shrinkage of the finished film in actual use.

In the manufacture of film base and the like it is desirable to extract the herein described resid ual low boiling solvents from cellulose ester film, either during the latter part of the casting operation or as soon after as practicable without destroying the structure of the film. For this purpose I use alcohol diluted as described herein in suitable proportions with water to regulate the swelling action and speed of extraction. In the second bath used to release the strain, I may add some compound such as methanol, ethyl or a higher boiling alcohol to hasten the release of the strain when a lower temperature bath is used or I may use some other liquid such as mercury which will not interfere with the subsequent drying of the film.

I have mentioned acetone as an example of a low boiling residual solvent in cellulose ester base because it is the solvent best suited for the manufacture or" nitrocellulose or cellulose acetate base and because it has not been successfully and rapidly extracted by prior methods. However. other low boiling solvents such as methyl or ethyl acetates or mixtures thereof would cause shrinkage troubles and these can also readily be extracted by my method. The following table of tests shows the effect produced by residual acetone contents on the shrinkage properties of film base;-

Percentage of gigi g shrinkage by film accelerated shrinkage test .z subsequently dried under no appreciable tension;

the other sample was not bathed. The bathed sample did not blush during the described shrinkage test, indicating that its properties are quite different from those of the untreated sample which revealed the usual blush. In addition the Percent acetone Pei cent after shrinktreatment treatment age Percent Treatment No treatment 20 min. in 90% methanol 15 min. in 90% methanol 15 min. in methanol 2. 3 Nil Trace Trace wcomp- From the foregoing it is evident that the solvent used to extract the acetone can not be classified except as one having a solvent action on the acetone or on other low boiling solvents in the film and also have no solvent action and only a slight swelling action on the film. Since methanol is a solvent for nitrocellulose film base it can not be used full strength to extract acetone therefrom; however, its solvent action thereon can be decreased by adding water or some non-sol vent for nitrocellulose, such as ethyl alcohol, without greatly aifecting its solvent action on acetone. Likewise since methanol is not a solvent for the type of cellulose acetate generally used in the manufacture of film base, it may also be used without dilution with water for extracting cetone or low boiling solvents therefrom. However, I have found that some dilution is preferable to decrease the solvent action of this bath on those softeners remaining in the film base which are not desired to be extracted. A wide choice of baths suitable for various types of base is thus afiorded.

Following are some samples of the effect of bathing film in methanol and in Water under different conditions that reveal some of the advantages of my improved method and improved products resulting therefrom Example 1 Samples of nitrocellulose film base .0075" thick were bathed 8 minutes in 90% alcohol under strain and dried under strain.

Per cent Potential shrinkage before treatment 1.6 Potential shinkage after treatment 1.8

Samples treated and dried under no strain showed a shrinkage of 0.2 to 0.4%.

Example 2 Samples of .0075 film base treated in 90% methanol and dried under strain were subjected to the action of a hot water bath under no strain, temperature 180 F. for 10 minutes. The potential shrinkage of these samples was thereby reduced to a range of from 0.04 to 0.2%.

Example 3 Samples of .0075 film base treated in 90% methanol under strain were heated in water at 180 F. for 10 minutes under various strains as follows- Potential shrinkage No strain 0.3 Under 700 grams strain 1.0

Under 1400 grams strain 1.2

No treatment 1, 1

I wish to state that my improved method of treating cellulose esters that includes extracting acetone and other low boiling solvents therefrom and which at the same time effects the release of potential shrinkage therein, is applicable to nitrocellulose powder, as well as to celulose ester sheets or castings suitable for the manufacture of phonograph record blanks or for the manufacture of containers for liquids such as milk. Containers fabricated from cellulose esters not subjected to my improved treatment would contaminate perishable liquids such as milk due to the presence of low boiling solvents in the cellulose esters of which prior containers are made, and furthermore such prior containers would soon become distorted by shrinkage. In cases such as those just described where it is not necessary or desirable to remove thetendency to blush, I prefer to first subject the sheets to a bath of hot water or hot moisture-saturated air at approximately 212 F. for from approximately ten minutes to approximately an hour in duration depending on the properties of the cellulose ester used and subsequently dry the sheets as described herein.

Having herein described a preferred embodiment of my invention, I do not desire to be limited thereto since it may be modified or applied in difierent'forms without departing from its spirit. It is expressly stated that this embodiment is illustrative only and that the invention is not limited to the materials, and specific elements described, but comprises all the equivalents thereof, and of 'the several cooperating features herein shown and described. Hence I desire to cover all modifications within the language or scope of any one or more of the appended claims.

What I claim as new and desire to secure by Letters Patent is:

1. The method of rapidly seasoning relatively thick products containing cellulose ester which includes the steps of extracting low boiling solvents therefrom by bathing in a solution of methanol and subsequently drying said thus treated products under only enough distention to prevent wrinkling or distortion thereof during said drying.

2. The method of rapidly seasoning transparent film base containing cellulose ester which includes the steps of subjecting said base to a bath containing asolution of approximately 90% methanol and 10% water and subsequently drying the thus treated base, under only enough tension to prevent wrinkling during said drying.

3. The method of rapidly seasoning transpar ent film base containing cellulose ester which includes the steps of subjecting said base to a bath containing a solution of approximately 90% methanol and 10% water, said bath being used at a temperature somewhat below the boiling point of methanol and subsequently drying the thus treated base, under only enough tension to prevent wrinkling during said drying.

4. The method of rapidly seasoning freshly cast transparent film base containing cellulose ester which includes the steps of bathing said base in a heated solution of approximately 90% methanol and 10% water while said base is under tension said bath having a temperature somewhat below the boiling point of methanol; drying said base under only enough tension to prevent wrinkling during said drying then bathing'said base in hot moisture saturated air at approximately 212 F. and subsequently drying under only enough tension to prevent wrinkling.

5. The method of rapidly seasoning sheets containing cellulose acetate which includes the steps of bathing in slightly diluted methanol and subsequently drying said sheets.

6. The method of rapidly seasoning transparent film base containing cellulose acetate which includes the steps of bathing in methanol and subsequently drying said base under only enough tension to prevent wrinkling during said drying.

'7. The method of controlling the shrinkage characteristics of transparent base containing cellulose ester, which includes the steps of extracting low boiling solvents from said base by means of a bath containing methanol while said base is under controlled tension, drying said base under a controlled tension, contracting said base in a hot aqueous bath at a temperature from approximately 100 F. to 212 F. under substantially no tension, drying said base under only enough tension to prevent wrinkling, and subsequently cutting and perforating said film.

8. A method of rapidly seasoning transparent film base containing cellulose ester which in' cludes the steps of first subjecting said base to a bath having a boiling point not higher than C. and composed principally of a solution of methanol, and subsequently drying the thus treated base under only enough tension to prevent wrinkling during said drying. I

1 MARTIN MARASCO. 

